Blitz, a pudgy old miniature schnauzer, seemed klutzy all of a sudden.

"He was constantly bumping into the cabinets, the furniture, everything," recalls his owner, Rosemary Kelly, of Chalfont.

This - and a spate of urinating indoors - concerned Kelly when she took Blitz to the veterinarian three months ago. She said Blitz also resisted climbing the porch steps at night to go inside, was less active, and no longer seemed to hear her voice commands.

While examining Blitz, the vet noted weight gain, a mildly enlarged abdomen, muscle atrophy, a dull and thinning coat, and yellowish discharge in both eyes.

During the appointment, Blitz bumped his head on the side of the exam table, prompting Kelly to ask whether he was going blind. Could it have something to do with his cloudy eyes? she asked.

Using an ophthalmoscope, the vet observed nuclear sclerosis in both eyes. This normal hardening of the eye lenses, which develops in dogs around age eight, lends a cloudy appearance to the eyes, but does not affect vision in any discernible way.

The vet saw pinpoint cataracts in both eyes, neither large nor dense enough to block vision. Also present was iris atrophy, a normal finding in a 14-year-old dog like Blitz. This age-related, degenerative change in the colored part of the eye produces a ragged outline to the pupil, but does not impair vision.

Blitz's pupils appeared dilated and did not constrict well when a light was flashed into them. And his tapetal reflection - "eye shine" - seemed brighter than normal.

A fluorescein stain test ruled out corneal ulcers; an antibiotic-steroid ointment was prescribed to treat the runny eyes.

The vet's main concerns were Blitz's unhealthy appearance and behavioral changes. The owner declined a urinalysis, but consented to blood work, which revealed hypothyroidism.

Among other things, hypothyroidism causes muscle wasting and mental sluggishness, and blunts nerve impulses, possibly impairing coordination. Could hypothyroidism explain Blitz's recent tendency to bump into things, his reluctance to go outside to urinate, and his decreased pupillary light response?

Was Blitz's apparent hearing loss causing his lack of response when summoned? Or were arthritis or dementia, common in senior dogs, the cause? But blindness - this was a long shot.

Blitz was sent home on thyroid supplementation, and his owner was referred to an ophthalmologist if his vision problems appeared to persist. And they did.

Solution:

A few weeks later, Blitz's eyesight seemed to worsen. So his owner took him to Shelby Reinstein, a board-certified veterinary ophthalmologist at the Veterinary Specialty and Emergency Center in Levittown.

Using special lenses to evaluate Blitz's eyes, she diagnosed progressive retinal atrophy (PRA). Blitz was going blind.

The retina, a multilayered sheet of neural tissue lining the back of the eye, consists of photoreceptors that convert visual images into electrical signals sent to the brain.

The retina contains two kinds of photoreceptors: "cones" that function in bright light, and "rods" that take over when the light dims. PRA causes the rods to die off first, so affected dogs first develop night blindness. They often refuse to climb stairs in the dark.

In Blitz's eyes, Reinstein noticed several changes associated with retinal tissue death: degenerated blood vessels, an extra-luminous tapetal reflection, cataracts likely caused by toxins from expiring cells, and pupils enlarged to allow added light to reach the waning rods.

"This disease progresses very slowly," Reinstein says, "so my gut feeling is that this dog's rods started to degenerate when he was about 10."

Why did Blitz's blindness come on so suddenly?

It didn't. If Blitz read books or threaded needles, he would have needed extra lighting and eyeglasses years ago.

PRA is a family of diseases caused by different mutations that lead to retinal deterioration and, ultimately, total blindness. Though rare, it has been described in a number of breeds, including Labrador retrievers, poodles, collies, Siberian huskies, Portuguese water dogs, Irish setters, and miniature schnauzers.

In cats, PRA mutations have been identified in the Abyssinian, Siamese, and Persian breeds. The human version of PRA, macular degeneration, differs in its causes and clinical course, and is generally more age-related than genetic.

The age of onset for canine PRA, a painless condition that affects both eyes equally, varies depending on breed and mutation. It can range from just a few months old to middle age.

Though PRA is irreversible and untreatable, there is some evidence that certain antioxidant supplements slow the retinal destruction and preserve eyesight for longer.

And with environmental modifications - keeping furniture arrangements intact, placing food and water bowls within easy reach, blocking stairwells with baby gates - affected dogs can maintain a good quality of life.

Blitz's vision has continued to decline. Each night, Rosemary Kelly carries him into the bed that he can no longer find. But she says he still seems to enjoy life.

Joan Capuzzi is a veterinarian at Cottman Animal Hospital in Northeast Philadelphia. She can be reached at jpcapuzzi@outlook.com.